The role of nicotine as a reinforcing agent in tobacco will be investigated as a function of several key variables: 1) smoking deprivation and satiation; 2) conditioned stimuli accompanying inhalation of nicotine; 3) other constituents in tobacco (tar); and 4) situationally induced anxiety (performing while being videotaped). While manipulating these influences systematically in the following experiments, nicotine's reinforcing value will be measured behaviorally using a smoke mixing device that allows subjects to adjust the nicotine delivery of each puff they take. Preferred nicotine levels, puffing and volume of smoke taken in will comprise the dependent measures of smoking. Our goal is to pinpoint the critical pharmacological and psychological variables mediating smoking satisfaction. In so doing, less harmful substitutes may be developed which preserve the reinforcers sought by smokers, and reduce the health risks to which they are currently exposed.